1. Field of the Invention
The present invention relates to a liquid crystal cell and more particularly to a cell wherein alignment layers of organic material are provided on those surfaces of the cell walls which face the liquid crystal material.
2. Description of the Prior Art
In certain liquid crystal cells, particularly in those with nematic and cholesteric liquid crystals, the cell walls which are in contact with the liquid crystal material must be provided with alignment layers to achieve the desired molecular orientation of the liquid crystals. As a rule, the alignment layers are deposited so that the molecules at opposite cell walls lie mutually at 90.degree.. As is known from DE-OS No. 29 45 641, DE-OS No. 29 16 670, and German Pat. No. 24 57 641, the alignment layer consists either of inorganic substances deposited by oblique evaporation in a vacuum or of organic substances applied by dipping, brushing, or spraying.
Alignment layers of inorganic material, such as calcium fluoride or silicon monoxide, are formed by evaporating the substances in a high vacuum at a very small angle to the substrate. Such layers are unsuitable for mass production because they require a very large amount of work and apparatus.
Alignment layers of organic substances are relatively easy to produce because the organic material, dissolved in a solvent, can be applied by dipping, spraying, or brushing, which necessitates only simple equipment. In such layers, the desired molecular orientation is achieved by subjecting the applied material to directional mechanical action, particularly to shearing forces, by treating the layer in a given direction with a brush, a roller, or a squeezer. The liquid crystal molecules then align themselves on such a layer by adhering at one end to the organic alignment layer. Various forces may arise during this alignment, such as Van der Waals forces, as is mentioned in DE-OS No. 29 16 670.
Unlike the oblique evaporation technique, however, the use of organic alignment layers does not make it possible to fix the tilt angle of the liquid crystal molecules.